Octanuclear cluster

A large series of heterocapped dianion clusters of general formula [Re7(CO)2i-(C)M(L)] (M = Pt, Pd, Ir, Rh L = Me2, allyl, 2-methyl-allyl, 1,5 cyclooctadiene. 

It is apparent that the insertion of the 3-capping fragment into the original heptanuclear Rc7 complex makes oxidation more difficult, and progressively more difficult on passing from rhodium to the rhenium. 

It often happens that predictions of the capacity of a cluster to exchange electrons are made simply on the basis of electron-counting rules, sometimes in conjunction with structural features. The aim of this review was to point out how the redox behavior of homo- and heterometallic clusters, even those which are isoelectronic and isostructural, can often be unexpectedly different. 

Theoreticians are invited to develop new approaches to account for the redox behavior of polynuclear heterometallic compounds. 

Catalysis and Dynamics and Physical Properties of Metal Clusters Edited by P. Braunstein, L. A. Oro P. R. Raithby Copyright WILEY-VCH Verlag GmbH, D-69469 Weinheim (Federal Republic of Germany), 1999 

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Compounds (I), (II), (III), and (IV) (Table 2) have similar crystal and molecular structures (Fig. le), characterized by the following the crystals of these compounds are made of octanuclear cluster fragments [Tc8Br4(/(-Br8]"+... 

Based on its method of synthesis and some of its spectroscopic properties, compound (X) belongs to the group of octanuclear clusters (I)—(IV). However, its exact structure is still undefined. According to most of its physico-chemical properties, compound (X) is similar to [Fe(C5H5)2]3 [Tc6(/j-C1)6C16]C12 and... 

Octanuclear cluster [Au8 P(C6H2Me3-l,3,5)3 6]2+ is prepared by reduction of the oxonium salt [0 Au P(C6H2Me3-l,3,5)3 3] in the presence of 3 atm of CO [4]. The structure shows a cluster core composed of a distorted Au4 tetrahedron in which two of the gold vertexes are also bonded to two other gold atoms. Six phosphine ligands are linked to the gold atoms of the unshared vertexes. 

Most octanuclear clusters are based on C-centered octahedral frameworks, contain two gold atoms and exhibit a variety of overall geometries [160, 318, 384, 395-397]. 

Two homometallic octanuclear clusters, [FegS CNBu1) ] [37] and [Fe8S8 (PCy 3)61 [37,38], have been isolated (see earlier discussion), as has the related heterometallic cluster [Mo2Fe6S8(PEt3)6(tccat)2] [70], The latter cluster is the first example of an Fe—S edge-linked, reduced MoFe3S4 double-cubane with Mo atoms at the periphery of each cuboid subunit. The reduced double-cubane core is stabilized by triethylphosphane coordinated to the Fe atoms. The utility of such materials as precursors to potential cofactor models, both structural and functional, has yet to be explored. 

Finally, cobalt carbide-carbonyl clusters have recently been isolated through a two-step synthesis. First of all, the well-known Co3(CO)9CCl is prepared from Co2(CO)8 and CCh, and then the hexanuclear carbide dianion [Co6(CO)i5C]2- is obtained in good yields (9) by further reaction with Xa[(, o(CO)4] in diisopropylether [see Eqs. (18) and (19)]. Further redox condensation between [Oo6(CO)i5C]2-and Co4(CO)i2 [see Eq. (11)] gives the square antiprismatic octanuclear cluster [Cdo8(Cdt )i8 C]2- (13). Both these carbide derivatives, as well as all of the other cobalt high nuclearity clusters, are sensitive to air and react with carbon monoxide at atmospheric pressure. 

Ru3(CO)12 with Pt(PBu )2 at room temperature affords 92 as the main product, whereas reaction in refluxing hexane affords small amounts of octanuclear cluster 93 and tetranuclear 94. The capped-pentagonal bipyr-amidal 93 contains 104 cluster electrons, or six fewer than predicted by the Polyhedral Skeletal Electron Pair Theory. Solutions of 93 slowly decompose to give a small amount of 93, together with Pt3(CO)3(PBu3)3. No platinum homologue of 91 has yet been isolated.63... 

A chemistry of cobalt-sulfide-thiolate molecular clusters comparable with that of iron systems has also begun to emerge. Treatment of [Co4( -SPh)6(SPh)4]2- with HS- in acetone affords the octanuclear cluster [Co8(ji4-S)6(SPh)8]4 isolated as its Pr4N+ salt.988 In MeCN solution the complex is red-purple with intense sulfur-core charge transfer bands which obscure the Co" d-d transitions. This behaviour contrasts with that of both mono- and poly-nuclear cobalt"-thiolate complexes, which all display LMCT bands below 440 nm and have well-developed v2 and v3 features. The [Co8(/j4-S6)]4+ core sustains reversible one-electron oxidation and reduction (E]l2 = —0.54, — 1.18 V, MeCN) and chemical reduction with sodium acenaphthylenide in THF gives [Co8(/r4-... 

Trifluoromethyl)phenylcopper was found to be an octamer by consideration of the kinetics of its decomposition, and by cryoscopy and vapor pressure osmometry in benzene solution 36). Its F NMR spectrum in ether at room temperature is a sharp singlet. Consequently, the suggested structure is a central copper cube with equivalent bridging benzotri-fluoride groups. The initial decomposition product, Cu8( n-CF3CgH4)e, is considered to be a Cu(0)—Cu(I) octanuclear cluster compound 36). For the octameric m-(trifluoromethyl)phenylcopper, the tetrameric ortho isomer, and pentafluorophenylcopper tetramer, the F NMR spectra were found to vary with temperature. The changes are not considered to involve important structural alterations, but only variations in solvent complexes and rotamer populations 32, 37). The spectra also... 

The X-ray structure analysis of bismuth thiosalicylate has revealed that the compound forms an octanuclear cluster core [Big(tsal)i2(DMF)6](DMF)6, where tsalH2 denotes a thiosalicylic acid unit. The presence of stereochemi-cally active lone pairs of electrons is suggested for each bismuth center [94CL2123],... 

An octanuclear cluster of copper has recently been prepared by the reaction of copper(II) bromide with the dianion of l,l-dicyanoethylene-... 

The bimetallic, octanuclear cluster Na2[Pd4 MoCp(CO)3 4] has been found to catalyze the dehydration of alcohols such as MeOH, EtOH, and Me2CHOH, to give carbene ligands. trauj-Stilbene was formed from PhCH20H. ... 

Pathways to neutral octanuclear clusters with and FeMo-cofactor-like topologies. Dmp = 2,6-dimesitylphenyl Tip = 2,4,6-triisopropylphenyl. 

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